Fat structure, composition, and configuration can influence cholesterolemia and atherosclerosis. Most studies of experimental atherosclerosis involve feeding fat and cholesterol to susceptible animal species, and the cholesterolemic properties of the individual fats are accentuated by the presence of the sterol. However, experiments using cholesterol-free diets give data that are similar with regard to the ej$ects of fats but considerably less extreme vis-a-vis cholesterolemia. Examples of the eflects of unsaturation, steric configuration, and triglyceride structure are discussed. (J. Nutr. Biochem. 6:172-178, 1995.) Unsaturated and saturated fats Anitschkow and colleagues'*2 in 1913 were able to induce atherosclerosis in rabbits by feeding cholesterol suspended in sunflower seed oil. For several decades thereafter workers in atherosclerosis considered the fat vehicle used for addition of cholesterol to the diet as a number of interchangeable entities. In the 1950s the level of dietary fat was perceived as the governing factor in human cholesterolemia. Keys et al3 demonstrated a strong relationship between the percentage of dietary fat and cholesterolemia in a number of ~pulations. However data were already accumulating to show that the type of fat (saturated or unsaturated) played an important role in human or animal cholesterolemia. Kritchevsky et al. 4*5 showed that a diet containing cholesterol plus an unsaturated fat was less atherogenic for rabbits than one containing a more saturated one. (Table 1). In 1958, Groen6 reviewed the studies of fat and its relation to cholesterolemia and cited early studies that showed the different cholesterolemic effects of saturated and unsaturated fats. In 1957, Ahrens et al.' fed human volunteers formula diets containing 40% fat and showed that as the iodine value of the fat decreased (toward greater saturation) the subjects plasma cholesterol levels rose. The iodine value is a measure of the degree of ~sat~ation of a fat and is a reflection of the amount of iodine needed to saturate the double bonds.
In 1965, Keys' and Hegsted' and their colleagues developed formulas to predict cholesterol levels that might be observed when dietary fat was changed. The Keys formula was:
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